Communication traffic relayed by a relay device like a repeater increases with significant increase of the number of wireless terminal devices. Accordingly, there is proposed a distributed wireless communication system which allows a wireless terminal device to select at least one relay device among plural relay devices which are connected one another via a predetermined communication line when the wireless terminal device communicates with another wireless terminal device. In such wireless communication system, each wireless terminal device calls through a channel of a repeater to establish a communication path with a communication-counterparty wireless terminal device. The repeater notifies information indicating whether or not the current channel is busy or idle to wireless terminal devices in an area through a communication frame which is a unit of radio signal.
According to patent literature 1, a wireless communication system includes plural pieces of transceiver means for exchanging a wireless communication across equal to or more than one channel and plural pieces of repeater means each for establishing a wireless communication with equal to or more than one piece of transceiver means. A wireless communication is completed by an information signal (voice or data information) and by a control signal (control information transmitted in accordance with a signaling protocol). As the control signal which is transmitted in a sub-audio band simultaneously with transmission of the information signal from a channel is relayed and transmitted, a wireless communication is carried out between the transceiver means and the repeater means.
Each transceiver means is programmed together with two channel numbers: one is for home repeater means and another is for second home repeater means. When the power is turned on, the transceiver means scans both home channel and second home channel to determine whether or not to monitor it. When an effective control message is detected in either of the channels, the channel where the effective control message is detected becomes a monitor channel. In this case, the chance of the home channel becoming the monitor channel and that of the second home channel becoming the monitor channel are equal. Unless no effective control message is detected in the monitor channel or unless a system which is programmed with a different site number is selected, the monitor channel remains unchanged.
Patent Literature 1: Japanese National Publication No. H4-504342
According to patent literature 1, because a control signal is transmitted across both home channel and second home channel and the chance of the home channel becoming the monitor channel and that of the second home channel becoming the monitor channel are equal, a configuration is not accomplished in which either one of the channels supports another channel.
In addition to the wireless communication system disclosed in patent literature 1, according to conventional distributed wireless communication methods and wireless communication systems which allow a wireless terminal device to select a repeater having an idle channel that is currently able to relay a communication among plural repeaters when wireless terminal devices communicate with each other, unlike a wireless communication system with an dedicated control channel independently from a communication channel, as each repeater bears an equal role, a configuration is not accomplished in which a repeater bears a relaying process instead of another repeater when a situation causing another repeater currently performing relaying process to terminate that relaying process occurs. Moreover, like patent literature 1, the situation causing the relaying process to be terminated is not limited to a case in which no effective control message is detected.
As explained above, the conventional distributed wireless communication system has relatively low fault tolerance.
The present invention has been made in order to overcome the foregoing problem, and it is an object of the present invention to provide a wireless communication system which has high fault tolerance and which includes plural relay devices, a wireless communication method thereof, a relay device and a wireless terminal device.
Moreover, it is another object of the present invention to provide a wireless communication system which enables a relay device to bear a relaying process instead of another relay device when a situation causing another relay device currently performing relaying process to terminate its operation occurs, a wireless communication method thereof, the relay device and a wireless terminal device.